Dry kiln



J. F. COBB Aug. 7, 1934.

DRY KILN Filed June 18, 1931 3 Sheets-$heet l 1 M (m -A BY y WM-ATTORNEY J. F. COBB Aug. 7, 1934.

DRY KILN Filed June 18, 1931 3 Sheets-Sheet 2 mw.v .-m o 1 0 1 1% g m whATTORNEY J. F. COBB DRY KILN Aug. 7, 1934.

Filed June 18, 1931 5 Sheets-Sheet 3 ATTORNEYX Patented Aug. 7, 1934 DRYKILN James Forrest Cobb, Portland, Oreg. Application June 18, 1931,Serial No. 545,345

8 Claims.

My invention relates to improvements in kilns having a main drive foractuating one or more transverse shafts on which one or more fans aremounted for driving the circulating medium in the kiln transversely tothe length of the kiln in continuing cross circulation throughinterstices provided in the stock loads.

An important object of my invention is to balance or substantiallyequalize the throw of the fans and thereby effect greater uniformity ofcirculation throughout the kiln. In other word, my invention iscontrived to cause a novel counteraction oitransverse circulatorycurrents of air within the kiln, with the result of effecting a moreuniform general circulation.

Another object of my invention is to provide novel driving means foraccomplishing the results desired.

Another object of my invention is to effect counteracting currents bynovel means in both forward and reverse directions of air circulationtransversely within the kiln, and thereby to accomplish a greateruniformity of distribution of the circulation through the interstices ofthe stock loads.

Another object of my invention is to effect a better mixing of thegaseous contents of the kiln by effecting some longitudinal circulationbetween the medial portions and the ends of the kiln in either directionof circulation in addition to the :general transverse circulation abovementioned. Another object of my invention is to provide novelcompensation means for permitting the 33 incidental expansion andcontraction of a drive shaft for one or more fans.

What constitutes my invention will be hereinafter specified in detailand succinctly defined in the appended claims.

In the accompanying drawings, in which my invention is illustrated inpresent preferred form of embodiment,

Figure I is a plan view of a kiln in which fans are illustrated aslocated above the material to be dried.

Figure II is a longitudinal vertical section on the line II-II of FigureI. p

Figure III is a transverse vertical section on lines III-III of FiguresIand II, respectively.

Figure IV is a plan view of another form of kiln modified in respect todisposition of the fans below the material to be dried.

Figure V is a longitudinal vertical section on the line VV of Figure IV.

Figure V1 is a transverse vertical section on the lines VI-VI of FiguresIV and V, respectively.

Figure VII is a side elevation of a gear and its support complete withcompensating means for permitting expansion of a drive shaft upon whichsaid gear'is mounted.

Figure VIII is a front elevation of the subject matter shown in FigureVII.

Figure IX is a side elevation of another form of embodiment of a geardrive for the Ian, illustrating modified compensating means forpermitting variation of the length of the drive shaft.

Figure X is a front view of the subject matter of Figure IX.

Figure 2G is a side elevation of a modified means for providingcompensation for expansion and contraction of a common drive shaft for aseries of fans.

Figure XII is an end elevation of the subject matter of Figure XI,looking from right to left.

Figure XIII is an end elevation of a kiln showing an individual motordrive for one of the fans located above the stock loads under a gabledtype or stream lined roof.

Figure XIV is a side elevation of a portion of the type of couplingshown in Figure XI.

Figure XV is a side elevation of a modification of means for providingcompensation for expansion and contraction of a common drive shaft forseries of fans.

Referring to the numerals on the drawings:

1 indicates a kiln floor, 2 and 3 its side walls, and. 4 its roof. 5indicates a non-indispensible intermediate partition disposedhorizontally between the fioor 1 and the roof 4, which is shown inFigure III as above, and in Figure VI as below the stock load. 6,wherever it appears, is a partially diagrammatic illustration of a stockload or loads of material to be dried. 9 and 10, Figure V, indicatedoors which, being disposable at discretion at either one or both endsof the ltriln, are kept closed while the kiln is in operaion.

The stock loads 6 are stacked in any suitable manner preferred. Forexample, they may be loaded upon bunks 12 which are supported as by drykiln trucks 13 that may travel on track rails 14 provided for theiraccommodation within the kiln. The rails 14 may rest upon track.supports 15 which may be cross ties resting on the ground or floor 1, ormay be'c'ross beams supporting the tracks above the floor 1, as shown inFigure V.

The stock loads 6 are preferably stacked by at 20 and 21,

aid of stickers 16 placed between layers of the stock in such manner asto provide interstices 1'7 between adjacent layers so as to permit freeair circulation within the kiln therebetween.

Heating means within the kiln are indicated They may be of any suitableform of embodiment or location whether commonly known in the art or not.

I employ circulation compelling equipment comprising, for example, fans25 and 26,-25 being used to designate right hand fans and 26 being usedto designate left hand fans. These fans are operatively mounted, forexample, on transverse shafts 27 and 28 which may be carried by bearings30 and 31 provided on hearingstands 33 and 34 (see Figure VI, forexample). The bearings are provided with means of lubrication such, forexample, as suitable oil cups 35 which may be, as preferred, either ofthe wick-feed type or of the duct-feed type. One of the bearings 30 or31 should be adapted to take end-thrust. In some cases, such as shown,for instance, in Figures, I, II and III, I employ a combination ofgears, 33, 39, 40, and 41, a case 44, bearings 46 and 4'7, and a support48 for the longitudinal shaft 37 and transverse shafts 27.

The combination of bevel gears or bevel friction, for instance, or anysuitable means, and their cases are designed, respectively, to operateright hand fans 25 and left. hand fans 26, respectively. Each gear case44 accommodates preferably bevel gears 38, 39, and 41, which may bespiral bevel gears, or the equivalent thereof if preferred. The gears 88and 40 are keyed or otherwise securedto the longitudinal shaft 37.

The gears 38, 39, v40 and 41, are assembled in pairs for imparting righthand or left hand direction of rotation to the shaft 2'7, as desired. Aright hand set of gears may include a gear 38 fixed on the common driveshaft 37 and a gear 39 keyed or otherwise fixed to a driven shaft 27.The left hand assemblage of gears consists preferably of a spiral bevelgear 40 fixed to the drive shaft 37 and a driven gear 41 fixed to thetransverse shaft 28 on which the left hand fan 26 is fixed.

The gears above mentioned may be substantially the same in all respectsexcept that one assemblage of gears 38 and 39 is employed for drivingright hand fans, and the other assemblage 40 and 41 is employed fordriving left hand fans.

The fans 25 and 26 are preferably mounted upon transverse shafts in apartition 52 extending substantially the full length of the kiln. Thepartition 52 has openings 54 and 55 for the accommodation of the rightand left hand fans, respectively, an they, are made sufficiently largeto permit movem nt of the fans due to expansion and contraction of theshaft 37.

In my kiln, of whatever type it be and whether it comprises one or morecompartments, the fans effect one circuit of circulation movingsimultaneously transversely throughout the full length of. a compartmentof the kiln in one direction or in the opposite direction. When thecirculating medium is moving in one direction,

the right hand fans 25 turn clockwise and the left hand fans 26,although they blow in the same general direction, turn counterclockwise.

In the state of the art prior to my invention, all right hand fans, orall left hand fans, when mounted on transverse driving shaft, have beenmade to rotate in the same direction fo PIO- ducing one circuit oftransverse circulation. The result of such arrangement in operation isan unequal transversely distributed circulation that is due to the throwor variable directional flow of air from all the fans in addition to thetransverse air movement. The combined throw of all the fans tends todevelop a greater volume and velocity of circulation locally within thekiln, which causes an uneven drying condition within thekiln that isobjectionable.

In one form of embodiment of my invention I propose to use alternatelydisposed right and left hand fans, respectively, which are rotated,respectively, in opposite directions. The throw of one of the fans is,therefore, counteracted by the throw of the next adjacent fan to such anextent that a substantially transverse air circulation is effectedwithin the kiln.

Right and left hand fans have been employed in kilns on one longitudinalshaft delivering counteracting currents \friom the respective fanstowards each other in order to effect a distributed transversecirculation within the kiln. My invention is differentiated therefrom bythe use of right and left hand fans, on separate transverse shafts,respectively, thereby eliminating the complication of the necessity forthe use of zigzag walled ducts or other obstructions which tend to buildup resistance and to,increase static pressure, thus decreasingcirculative air flow. By using transverse driving shafts and right handfans and left hand fans alternately disposed through the kiln androtated in opposite direction, alternately, I am able to obtain maximumair circulating efiiciency, uniform distribution of transverse aircirculation, a thorough mixing of the circulatory medium, including thefresh air which has been taken on the suction side of the fan, and auniform distribution of humidity. from the source which supplies it,also a uniform distribution of the circulating medium in operativecontact with the heating coils of the kiln, so as to uniformly heat,mix, and humidify the circulatory medium before it passes into dryingcontact with the stock.

In another embodiment of my invention, I propose to use a series ofright hand fans at one end of the kiln and'a series of left hand fans atthe other end of the kiln. The right hand fans are disposed in series toeffect by counteraction of two or more series, one general circuit oftransverse circulation within the kiln.

When the right or left hand fans are em-v ployed in series, the fanthrow effects a resultant longitudinal trend of circulation toward theends of the kiln or toward the medial portion from the ends in twocircuits of circulation in addition to the general transversecirculation.

There are forms of embodiment of my inventaion in which I prefer to useone driving shaft 37 to rotate all the fans by means of gears preferablyof the bevel type or other like means which may be right hand or lefthand, and corresponding transverse shafts on which corresponding rightand left hand fans are mounted, which will thus be rotated to the rightor to the left, depending upon the arrangement of the said gears.The,.right hand gear 38 or the one rotating to the right or in clockwisedirection of movement, will drive a right hand fan 25, and the left handgear, 40, rotating to the left will drive a left hand fan 26. Theseright hand and left hand gears may be alternately disposed, or the righthand gears may be of expansion and contraction of the drive shaft 37,are provided, such, for example only, as sliding gears on the gearsupports, or gear supports which may be pivoted to permit expansion orcontraction of the shaft.

In some cases (see Figures IV, V, and VI) where a continuous shaft 37drives a series of fans by means of gears having transverse shafts 27and 28 at right angles to the longitudinal axis of the kiln, the shafts2'7 and 28 may be supported by one or more bearings 30 and 31 of whichone may be located beyond the fans. In some cases the shaft support maybe mounted on the inside of the inside or other wall of the kiln, or itmay be mounted even outside the kiln.

In some cases, I prefer to provide suitable means for cooling the gearswhich may, for instance, consist of extension of surface radiation 58,of familiar use in the art, as shown in Figure IX.

In case an endless chain or rope 60, or individual motor 73, isemployed, as it maybe, (see Figure V) to drive the cross shafts 2'1 and28, the same may be located wholly or in part either inside or outsideof the kiln.

In some cases, also, I place fans adjacent to the end doors or otherdoors of the kiln in such a way that a fan throw is made against thedoor, thus effecting a uniform pneumatic pressure against thedoor andconseqent di charge out through the crevices around the door inpreference to effecting an intake of air therethrough. Thus, by buildingup pneumatic pressure at the door, admission or intake of cold airthrough the crevices is in large measure prevented with the result of amore uniform drying in the kiln operation. The fans may be driven byindividual motors 62, in which case the same combination of oppositepitch of fan blades will be available through opposite rotation of thetransverse shafts 27 and 28 to effect within each kiln compartmenttransverse movement of circulation.

The fans may be at discretion disposed overhead, at the side of theloads, or below the loads, as preference may dictate.

The coils 2021 may be heated by any suitable'means, as for examplefrom'any preferred source of steam supply not illustrated. Power tooperate the shaft may also be derivedfrom a source not illustrated. Thestock loads of lumber 6 may be sta cked, if preferred, in any suitableor commonly used manner.

The drive mechanism may be, as already specified, by individual motor 62for each fan, or by one drive system, such as one continuous rope 60,cable, or other flexible element, as illustrated in Figure V forexample. In'other cases, eacli shaft mayhave a separate drive 62 foreach individual fan, or any other suitable driving mechanism may beemployed.

A plurality of two or more fans is designed to be employed in each kiln.If an odd number of fans is employed, the majority of them will beeither right hand or left hand fans, and in that case the resultantthrow of the combination fans may not be strictly transversely directedwithin the kiln, but the resultant throw may be directed towards thepart of the kiln that is, without provision to the contrary, ordinarilycoolest, by reason of in-drafts of outside air, excess loss of heat, andto outside exposure, or of other cooling factors.

I prefer to employ besides any usual system of heating coils 20 and 21,means for humidification 64 and any usual or preferred means forcontrolling the temperature and humidity within the kiln.

I prefer, also, to employ any usual means for admitting fresh outsideair, for exhausting the kiln atmosphere, or for the purpose ofventilation. If overhead fans are employed, I prefer to provide freshairports 66 and ventilators 67 on opposite sides of the respective fansat points of suction and pressure, respectively. The fresh air ports 66and ventilators 67. may be located at points developed by them ofmaximum suction and pressure, but they may, if desired, be placed in anyother suitable and desired relationship to the fans. For instance, theymay be placed at points of maximum pressure in some installations andpoints of minimum pressure in other installations, depending upon thedesign of the kiln, the location of the fans, and other considerations.The fresh air ports 66 and ventilators 67 may, in some cases,,requireair direction ducts in addition to mere ports.

My kiln may be either of the charge type or of the progressive type, theprinciples involved in my invention not being limited to any particulartype of kiln. Furthermore, the principles of my invention may be appliedto kilns having longitudinal as well as kilns having transversecirculation effected as by means of fans having shafts substantiallyparallel to the air flow.

In various embodiments of my invention, I prefer to employ partitions 52between fans to prevent back-lash or short circuiting of air betweenfans instead of air flow passing through the stock loads. I also preferto provide suitable baffies 70 and 71 at the ceiling and at the floorrespectively, to prevent air from passing around the stock loads insteadof through them, as preferred of course.

In the usual installation of any form of embodiment of my invention, thefans are mounted in close proximity either to the fioor 1 of the kiln,or to the roof 4. The space between each fan and the partition 5 variesin most-installations so as to provide a greater spacing between theedge or periphery of the fans and floor 1 or the roof 4 of the kiln thanbetween the edge of the fans and the partition 5 of the kiln or the topof the stock load 6. This variation of the position of the fans inrelation to deflecting surfaces permits each fan in rotation to deliverair in slightly variable direction in addition to the prevailingtransverse movement of the air. This variable or longitudinal tendencyof the air movement, in addition to the general transverse air movement,is known as throw and inasmuch as the fans are substantially all spacedequally from the side wall partition or stock loads within the kiln, thethrow from a right hand fan is substantially equal and opposite to thethrow of a left hand fan. By the change of direction, the. counteractingcurrents from the oppositely rotating fans substantially merge into onecurrent before passing through the stock.

The usual fan throw varies in direction and extent. There is what may betermed a normal tendency toward a throw in most instances, and thecounteraction of this throw is contem- One of the main objects of myinvention is to provide for counteracting this fan throw as justspecified. Such counteraction may be effected in at least one of twoways;-first, either by alternating right and left hand fans throughoutthe kiln; and, second, by placing right hand fans in series at oneportion of the kiln and left hand fans in series at the other end orportion of the kiln. In the first of these cases, the tendency towardsresultant throw or towards directed longitudinal circulation issubstantially eliminated. In the second case, the series of fans in one,portion of the kiln may effect a resultant throw in one direction, butthis would be counteracted by the substantially equal and opposite throwof the other series of fans in the same compartment of the kiln inanother direction. Upon reversal of the fans, the resultant throw ineach case would be substantially directed in opposite directions.

When an odd number of fans is used, the

odd fan is placed to throw additional air toward the part of the kilnthat is normally the coolest.

This is usually the low' end of the kiln or the door end of the kilnwhen only doors at one end are used.

A simple means for driving the fans is illus-/ trated in Figures IV, V,and VI. -These figures illustrate alternately d.sposed right and lefthand fans driven by-a common drive rope or chain 60, turning individualsheaves or sprockets 61. The rope or chain 60 is driven by suitabledriving means as, for example, a motor '73. A suitable tensioncontrol-assembly 74 is employed, consisting, for example of a weight 75for keeping'the belt 60 taut and so maintaining uniformity of tension onthe drive rope 60 by means of a pulley 76.

Illustrated in Figures I, II and III is a drive shaft within a kilnhaving bearings at spaced intervals for rotating one or more fans, whichshaft has a substantially fixed dispositional re lationship to thebearings or to the bearings and gears. There must be means for providingcompensation for expansion and contraction of the shaft, and in additionthereto, for maintaining this above mentioned fixed dispositionalrelationship. This may be done in one of several ways, of which, forexample, ,four are illustrated.

In the form of embodiment of my-invention illustrated in Figures I, IIand -III, I employ, as

.aforesaid, a common longitudinal drive shaft 37 for the fans. At thatend of the kiln where the motor is located, which, when a common driveshaft is used, may be, therefore, denominated the drive end of the kiln,I prefer to provide one thrust bearing Z7 which accommodates the shaftat that point which'is preferably close to the drive mechanism or motor'78. A result, substantially the same as that already described, isachieved in this kiln, insofar as right and left hand fans turn inopposite directions to deliver air in the same general transversedirection. The driving of the shaft may be accomplished substantially inthe manner described above. In my system, it is necessary to providemeans permitting compensation for expansion and contraction in a fanshaft such, for example, as the main drive shaft 37, so that nodisturbance of the operative relationship between the driven fan andshaft is occasioned by shaft expansion or contraction. In the drawings,I illustrate four means of accomplishing this result.

7 For instance, in .Figures VII and VIII, I show a gear and shaftsupport having a base which may be for stability firmly attached to thesub-floor 5. The top part 81 of said base supports in constant operativerelationship the gear case 44 and bearings 46 and 47, and is joined tothe base by suitable means, such, for example, as'bolts 83, having eacha cotter pin 84. When this type of bearing and gear stand is used,expansion or contraction of the main drive shaft 37, due to variation oftemperature, effects a movement of the shaft by means of movement in thejoints 85 and 86. In the normal kiln, which is usually less than 120feet long, the maximum expansion or contraction due to change intemperature would be less than two inches, which would measure themaximum movement of the bearing and gear required at the end of the kilnopposite the thrust bearing.

In Figures VII and VIII, I show pedestal joints providing for movementof the shaft and its bearings, or its bearings and gears to allowexpansion and contraction of the shaft 37. The shaft expansion orcontraction is substantially uniform and the movement of the severalbearings, or several bearings and gears, respectively, is proportionalto the distance from the thrust bearing of the driven end of the shaft.amount of expansion, for instance, will determine its horizontalmovement from the thrust bearing. Because the bottom of the pedestal isfixed, each bearing or bearing and gear will describe an arc of acircle, its travel being proportional to amount of expansion. In thecase of any material amount of expansion or contraction possible in theoperation of the kiln, the shaft will remain substantially straightbecause the are described by the bearing or gear having the greatestmovement will not be great enough to materially affect the alignment ofthe shaft.

In Figures IX and X, I illustrate another compensating means forproviding for shaft expansion and contraction. This means includes asliding gear case 88 and its pedestal 89. In other words, when expansionor contraction of the shaft 37 permits .the gear case 88, which isfixedly attached to said shaft but is loose on its pedestal, to slide inthe groove 90 of its pedestal 89, thus taking care of any shaftexpansion and contraction that may occur.

This expansion and contraction can be compensated for and taken care ofin a number of ways, for example, illustrated in Figures XI and XII.This third method of taking care of expansion and contraction of theshaft, consists of a jaw type coupling 92 mounted between intermediatecombination bearings and gear cases 44 and 45. In this case the bearingpedestals 48 form rigid supports for the bearings and gear cases 44 and45. Each gear case 44 and 45 is thus attached to a divided section ofthe shaft 37, each section being joined to the section adjacent by meansof the jaw type couplings 92 with suiiicient clearance 93 between halvesof the couplings 92 and ends of the shafts, to provide for requisiteexpansion and contraction in each section of the shaft.

Right hand and left hand worms may also be employed for accomplishingthe same compensation for expansion and contraction of the shaft, asshown in Figure XV. The worm 68 is long enough to permit maximum expan-The" sion of the shaft 37 and still permit engagement with the wormwheel 69.

The worm wheel will drive the transverse shafts, comparable to shafts 27and 28 in Figures VIII and IX. y

In all cases where a common drive shaft 3'7 is used, the fans move withthe shaft and provision must be provided for this movement in the fanhousings. Any preferred method may be employed for this, for example, Ihave illustrated a fan housing slightly large to provide plenty of spacefor the movement of the fans due to expansion or contraction. The fanopenings may be elliptical.

Any preferred housing for the fans may be used, such for example, asstream lined, band housing, or plain openings in the partition.

It is to be understood that the compensation for expansion andcontraction of the shaft may be employed in other instances than thoseillustrated. For instance, it may be employed, if need be, for a shafthaving fans mounted directly on and rotated directly with the shaft.

If more than one common drive shaft, or series of transverse shafts, isused, all the resultant throw of all the fans would be coordinated toeffect the most effective and uniform drying conditions.

I prefer to provide suitable baffles 70 and '71 which prevent thecirculating atmosphere from evading the loads in making circuit.

I also prefer to provide suitable fresh air intake ducts 94 andventilators 6'7 of any form preferred, such, for example, as those wellknown in the art. When the fans are located below the stock loads asshown, for instance, in Figures IV, V, and VI, fresh air ducts 94 havingintake doors 95 opening to the outside of the kiln and ports 96 openingat each fan, are preferably provided. It is to be understood that whenthe circulation is in one direction, the air duct on one side of the fansupplies fresh air, and when the circulation is reversed,

- the ports on the other side of the fan functionate by substitution forthe .ducts. In each case the fresh air duct or the port on the suctionside of the fan is employed to admit fresh air into the kiln. When thefans are placed above the loads, as shown in Figures 1, II, and III, Iprefer to provide ports on. opposite sides of each fan which act eitheras fresh air ports or as ventilators 66 and 67, respectively, accordingto the direction in which the air of circulation is moving. When the airis passing in one direction, the ports 66 act as fresh air intakes andthe ports 67 on the opposite side act as ventilators. When thecirculation is reversed, the relationship of the fresh air ports andventilators is correspondingly reversed. It is understood that in kilnshaving fans above the stock loads, the roof construction may be flat,arched or gabled, to provide stream line air guiding surfaces ifdesired.

The operation of the kiln requires the setting of the fans in motion todeliver in effect air in one circuit of transverse circulationthroughout the kiln. Fans rotating in relatively opposite directionscounteract any tendency towards unequal effective distribution ofcirculation.

As the kiln-becomes heated up in operation, the line shaft 37 tends toexpand. This is compensated for by means already described withreference to Figures VII and VIII.

It is my intention that this invention be not confined to the exactdesigns shown, as there are many ways of carrying out the sameprinciples which will readily suggest themselves to one skilled in theart. Therefore, it is to be understood that this invention includeswithin its scope whatever arrangements come within either the terms orpurview of the following claims.

What I claim is:

1. In a dry kiln, right and left hand fans, each of said fans effectingindependently by'delivery of an air current circulation of thecirculatory medium through the interstices of the stock loads in onecircuit of continuous circulation, right hand fans turning in oppositedirection from the left hand fans.

2. In a dry kiln comprising circulating means distributively mounted inseries throughout the length of the kiln on separate shafts, a commondrive means for said shafts, said circulating means consisting of rightand left hand fans turning in opposite directions for effecting onesubstantially uniform circuit of air circulation through interstices ofstock loads within said kiln.

3. In a dry kiln comprising circulating means mounted on separateshafts, a common drive means for said shafts, said circulating meansconsisting of right and left hand fans operatively mounted substantiallyin one plane, said fans turning in opposite directions for effecting onesubstantially uniform circuit of air circulation through interstices ofstock loads within said kiln and meansof providing compensation forexpansion and contraction of said shaft.

4. In a dry kiln, right and left hand fans alternately disposed withinthe kiln, right hand fans turning in opposite direction from the lefthand fans, all of said fans effecting circulation of the circulatorymedium through the inter-, stices of the stock loads in substantiallyone circuit of circulation.

5. In a dry kiln, right and left hand fans disposed respectively inseries at opposite ends of the kiln, right hand fans turning in oppositedirection from the left hand fans, all of said fans effectingcirculation of the circulatory medium through the interstices of thestock loads in substantially one circuit of circulation.

6. A dry kiln comprising within it a drive shaft, a thrust bearing forsaid drive shaft, a plurality of gears fixed at intervals along saidshaft, a journaled bearing for said shaft, a plurality of driven shaftsat right angles to said drive shaft, each supported by a bearing andhaving a gear fixed thereon operatively enmeshed with and driven by oneof the gears fixed on said drive shaft, a case for each pair of'gears, asupport for each of said cases, a fan on each of said driven shafts,means providing for expansion and contraction of said drive shaft andmaintaining variable longitudinal relationship of said cases on theirsupports and constant operative relationship between each pair of driveand driven gears, whereby said fans are rotated in either directionindependent of expansion or contraction of said drive shaft due tovariation of temperature within said kiln.

7. In a dry kiln, a partition, a right hand and a left hand fanoperatively disposed in openings provided in said partition, each ofsaid fans effecting an individual circulation, the right hand fanrotating in the opposite direction from the left hand fan whereby onecircuit of continuous circulation is effected through interstices ofstock within said kiln.

cases, means providing for variable movement of said cases, a partitionin said kiln having openings therein for the accommodation of-said fans,and means for maintaining a substantially constant longitudinalrelationship between the gears of each of said pairs whereby a variablelongitudinal relationship exists between each of said-fans and itsrespective opening in said partition depending upon the expansion andcontraction of said longitudinal shaft.

I JAMES FORREST COBB.

